1. Field of the Invention
The present invention relates to a rehabilitation system for use by orthopedic patients after fracture injury or joint replacement, by patients inflicted by neurological conditions such as cerebral vascular accident (CVA) and cerebral palsy (CP), by patients subsequent to lower limb amputation, and by patients rehabilitating from sports injuries such as meniscial, ACL or achilles tendon tears and, more particularly, to a portable, self-learning adaptive weight bearing monitoring system for rehabilitative use by such patients.
2. Description of the Prior Art
In the United States alone, millions of people each year suffer from serious leg injuries that require prolonged physical therapy. More than 500,000 hip and knee replacements are performed every year. Also, over 250,000 hip fractures, most of them requiring open reduction and internal fixations, are noted yearly in the United States. In addition, the number of multiple trauma victims with lower extremity fractures that require rehabilitation is also substantial. Many individuals who have suffered a stroke also may be required to relearn the ability to control their body in a three-legged stance. Indeed, there are estimated to be almost 9,000 rehabilitation and physical therapy units in the United States that address such injuries and more than twice that number worldwide.
During the rehabilitation of a simple fracture, the conventional medical approach has been a partial weight bearing (PWB) approach. The PWB approach is recommended when a soft callus is evident on an x-ray typically taken 2 to 6 weeks after the injury. However, in the case of a complicated fracture, such as an intra-articular injury, the weight bearing is typically completely prohibited until 3 months post-injury, and only then is the PWB approach prescribed. While weight bearing is essential for the bone building process, an overload can damage the bone fixation and the healing process. Hence, PWB as a prescription is problematic because it is subjective and the patient must decide by himself/herself how much to load the injured limb.
However, several devices are known in the prior art that assist the therapist and patient in determining how much weight is being applied to a patient's lower extremity and include external limb overload warning devices that warn the patient of an overload or an underload in the amount of pressure placed on the leg. For example, Schmidt et al. describe in U.S. Pat. No. 5,619,186 a foot weight alarm device including a foot-shaped insole device including resistive force sensors that fits inside the patient's shoe to warn the patient when the patient is putting too little or too much weight on a limited weight bearing foot. The foot weight alarm device also includes a shoe pouch which laces in the shoe, a foot weight alarm unit which fits in the shoe pouch and contains electronics that connects to the insole device, a data cable that is used by a health care professional to program the foot weight alarm unit, and a foot weight alarm calibration system used by the health care professional to program the foot weight alarm unit. The foot weight alarm unit measures the forces on each insole's sensors to compute the total force, and when the total force is below the target value, a low tone is produced by the foot weight alarm unit, while in the target zone a high tone is produced and above the target zone a two-tone warble is produced to inform the patient to take weight off the limb. Other features of the Schmidt et al. foot weight alarm device include an optimal data-logging feature that logs the time and maximum weight of each step for up to 16,000 steps. This feature provides the physician with the ability to review the patient's progress while at, and after leaving, the rehabilitation facility. In addition, a motion detector turns on the foot weight alarm device when the first step is taken by the patient, and power saving electronic circuitry turns the device off when there is no weight on the foot, thereby saving energy.
Unfortunately, the foot weight alarm disclosed in the afore-mentioned Schmidt et al. patent is limited in that it is passive and provides limited information to the patient and the physician. In particular, while the foot weight alarm device provides biofeedback data relating to the weight force applied to the foot, it does not provide electrical stimulation to adjust the patient's gait. Rather, only a passive alarm is provided. In addition, the rehabilitation program using the foot weight alarm device is, by necessity, based on a subjective estimation of the maximal weight bearing the foot may accept, as opposed to objective parameters that are personalized to the patient. Moreover, the foot weight alarm device requires continuous professional supervision. A sensor device is desired that allows the patient to continue his or her rehabilitation program at home without the need for such continuous professional supervision.
Other weight sensor devices are also known which allow the physician to monitor the force applied to a lower extremity by a patient. For example, the so-called "ForceGuard" described in U.S. Pat. No. 5,107,854 has been used in the prior art to sense the amount of weight applied to the plantar surface of the foot. This device alerts the wearer and/or therapist with a repeating tone when the weight exceeds the pre-elected value. Typically, the ForceGuard device is used to train patients in limited weight-bearing accurately and consistently to the physicians' order, to report the results of training, and to provide data for consideration by monitoring physicians. In use, the physician's orders may be pound limits, percentages of body weight, or other phrases. Typically, the pound limits are rounded to the next lower setting on the ForceGuard weight-bearing monitor, where a typical setting is 20, 30, 50, 70, or 90 pounds. When the percentage of body weight limit is set, the setting is calculated by multiplying the total body weight by the percent ordered. As before, the percentage limit is typically rounded to the next lower setting on the ForceGuard weight-bearing monitor. In the ForceGuard device, toe touch weight bearing is interpreted as 20 pounds, unless the physician states otherwise. A toe touch pattern is accomplished with normal gait and stance, but less than 20 pounds force through the lower extremity. On the other hand, partial weight bearing is interpreted as 30 percent of patient body weight unless the physician specifies a different limit.
By way of example, ForceGuard Model 2090 consists of 3 components including an electronic module, a foot pad, and a leg band. The leg band is worn around the patient's ankle, and the electronics module is attached to the leg band. The foot pad, a flexible, fluid filled chamber, plugs into the electronics module and is worn under the plantar surface of the patient's foot inside suitable footwear. The foot pad senses the weight being placed through the patient's lower extremity. The electronics module functions as the user interface that processes information from the foot pad and produces an alarm when the weight on the foot pad exceeds the selected weight.
While the ForceGuard device and other weight monitoring devices are known in the art that measure, in one fashion or another, the forces that are applied to a patient's foot, no devices known to applicant provide sensory stimulation, such as electrical or mechanical vibration, that affects the patient's gait or provide a personalized rehabilitation program whereby objective parameters may be used to personalize the rehabilitation to the patient without the requirement of continuous professional supervision. A device with these and other improved characteristics is desired.